1. Field of the Invention
The present invention relates to an organic EL (Electroluminescence) display and a method for producing the same.
2. Discussion of Background
Research and development have been actively conducted on organic EL displays using an organic EL device. Organic EL displays are expected to be the next generation of displays because of having a wider viewing angle range and faster response than liquid crystal displays and because of an organic substance having a variety of light emission properties. The organic EL displays are configured so that a plurality of anodes are formed on a substrate, organic multi-layer thin films are formed on the anodes, and a plurality of cathodes are prepared on the organic multi-layers so as to be opposite the anodes formed on the substrate. The organic EL displays are current-driven devices, which emit light by themselves when a current is supplied to the organic substance layer provided between an anode and a cathode.
When an organic compound is laminated on electrodes formed on a substrate, an organic material is vacuum-deposited to form an organic compound film in some cases. In a case of vapor-depositing the organic material, when electrodes as a foundation layer for the organic compound film have a foreign substance adhering on or a projection or a recess formed on a surface, the organic compound film is not formed in a desired state because of the influence of the foreign substance, the projection or the recess.
As a method for solving this problem, there has been known a technique wherein a desired organic compound layer is formed by dispersing or dissolving an organic material for the organic compound film in a liquid and applying the dispersed or dissolved organic material as a solution to cover a foreign substance, a projection, a recess or the like (a wet application method, hereinbelow, referred as to the application method). For example, JP-A-2001-351779 discloses in paragraphs 0012 to 0017 and in FIGS. 1 and 2 that at least one film among organic compound films is formed by the application method.
Examples of the application method are an offset printing method, a relief printing method and a mask spray method. In the offset printing method and the relief printing method, a layer, which comprises a solution having an organic material dispersed or dissolved in a solvent, is formed only in a certain region. In the mask spray method, e.g. a metal mask, which has apertural areas formed so as to conform to desired regions, is disposed, and a solution, which has an organic material dispersed or dissolved therein, is sprayed. In the latter case, the solution is turned into mist by dispersing the solution in a gaseous medium, such as nitrogen, or using a two- fluid nozzle or the like.
In organic EL displays, separators (hereinbelow, referred as partition walls) are formed to separately prepare cathodes to be formed on an organic compound layer (see the publication). FIG. 6 is a cross-sectional view showing an example of the partition walls, which are disclosed in the publication. After anodes 2 are formed on a substrate 1, the partition walls 5 are disposed. For example, the partition walls 5 are formed so as to have the cross-section widening as the distance from the substrate 1 increases. This sort of the partition wall structure is called an inverted tapered structure or an overhang structure. By providing the partition walls 5 with such an inverted tapered structure, it is possible to more reliably separate the cathodes. When organic compound multi-layers (a hole injection and transport layer 13, a light emitting layer 14 and an electron injection and transport layer 15) are formed by the application method or the like in such state that the partition walls 5 have been formed, the respective organic compound multi-layers are separated by the partition walls 5, and consequently the respective organic compound multi-layers are formed in the gap between adjacent partition walls 5. After that, the cathodes 7 are formed by a vapor deposition method or the like. Since the cathodes are also separated by the partition walls 5, the cathodes 7 are formed as patterned cathodes 7.
In some cases, an insulating film having apertural areas is formed on the anodes to determine positions serving as display pixels by the apertural areas. FIG. 7 is a schematic view showing an example wherein an insulating film having apertural areas is formed in the structure disclosed in the publication. The schematic view shown in FIG. 7 shows the appearance of the substrate, which is observed from the side of a substrate with the electrodes formed thereon. FIG. 8 is a cross-sectional view taken along the line VIII-VIII of FIG. 7. FIG. 7 also shows components, which are hidden by cathodes and the like formed as upper layers.
In the example shown in FIG. 7, at first, anodes 2 and cathode connection terminals 3 to be connected to the cathodes 7 are first formed on the substrate 1. Subsequently, an insulating film 4 having apertural areas 4A is formed. The apertural areas 4A are formed at positions where the anodes and the cathodes are expected to intersect. Partition walls 5 are formed so as to be orthogonal to the anodes 2. Then, solutions containing different organic materials are applied or vapor-deposited to form organic compound layers 6. Although multi-layers are formed as the organic compound layers, the multi-layers are collectively shown by a single organic compound layer 6 in FIG. 8. The respective solutions are prepared so that the concentrations of the respective organic materials are adjusted so as to form the respective organic compound multi-layers in desired thicknesses in regions to form the respective organic compound multi-layers. After forming the organic compound multi-layers 6, the cathodes 7 are vapor-deposited on the top of the laminated organic compound multi-layers. The partition walls 5 serve as separating the organic compound layers 6 or the cathodes 7 into sections, forming the organic compound multi-layers 6 in the gap between adjacent partition walls 5 and forming the patterned cathodes 7.
On the side of the substrate 1 with the electrodes formed thereon, a second substrate (not shown) is disposed in a confronting way. A seal (not shown) is applied on an outer peripheral portion of a region of the second substrate, which is opposed to the organic EL device on the substrate 1. The substrate 1 and the second substrate are bonded together by the seal. The organic EL device is protected from exposure to moisture or oxygen by sealing functions given by both substrates and the seal.